As a conventional strain sensor of this type, the one disclosed in the microfilm of Utility Model H4-265 (Japanese Laid-open Utility Model H5-57605) is well-known.
A conventional strain sensor will be described in the following with reference to the drawings.
FIG. 13 is a perspective view of a conventional strain sensor.
In FIG. 13, sensor substrate 1 made of metal has first fixing hole 2 at one end and second fixing hole 3 at the other end, on which is disposed strain detecting sensor 4 having a thin gauge for detecting strain in a lengthwise direction.
Also, strain detecting element 4 is electrically connected to element section 5 and is also provided with lead 6 outwardly extended.
The operation of a conventional strain sensor configured as described above is explained with reference to the drawings.
As shown in FIG. 14, sensor substrate 1 is fixed by male screw 9 onto detecting member 8 provided with a pair of female screws 7. In this case, taking into account the variation of pitch of the pair of female screws 7 formed in detecting member 8, the inner diameters of first fixing hole 2 and second fixing hole 3 are a little larger than the outer diameter of female screw 7 so that sensor substrate 1 can be reliably fixed on detecting member 8.
In this condition, when an external force is applied to detecting member 8, sensor substrate 1 is deformed in accordance with strain in detecting member 8. As sensor substrate 1 is deformed, resistance value of strain detecting element 4 disposed on the top surface of sensor substrate 1 varies. The variation of the resistance value is taken out from lead 6 in the form of voltage variation when a current flows to detecting element 4. In this way, the external force generated at detecting member 8 is detected.
In the conventional configuration described above, the inner diameters of first fixing hole 2 and second fixing hole 3 are a little larger than the outer diameter of female screw 7. Therefore, it is possible to reliably install sensor substrate 1 onto detecting member 8. On the other hand, when an external force is applied to detecting member 8, the installing position of sensor substrate 1 shifts in the lengthwise direction of sensor substrate 1. This causes the position of end portion 10 of male screw 9 being in contact with the top surface of sensor substrate 1 to be shifted. Accordingly, the bending stress applied to strain detecting element 4 is varied as well. As a result, the output accuracy of the strain sensor will be deteriorated.